Recently, an information storage apparatus such as hard disk drives (HDD) has been required to have a rapidly increased storage capacity, and there has been an increasing demand for improvements in the recording density. There is rising concern that the increased recording density may frequently cause a problem that information that has been recorded in a track adjacent to a track in which information is being recorded by a recording head may be erased. This problem is called adjacent track erasure (ATE) or side erasure.
There is a proposal to arrange magnetic shields on both sides of the magnetic pole of the recording head to absorb the magnetic fluxes towards the adjacent tracks and to thus restrain the adjacent track erasure (see Japanese Laid-Open Patent Publication No. 2005-190518: hereinafter Document 1).
There is another proposal to project laser light having a diameter less than the width of the magnetic pole of the magnetic head onto a target track for recording and to thus heat the target track. The heated target track for recording has reduced coercive force and causes the effective width of the target track to be less than the actual width (see Japanese Laid-Open Patent Publication No. 2000-251202: hereinafter Document 2).
It is desired that the intensity distribution of the magnetic field generated by the recording head rapidly rises at the boundary of an area in which information should be recorded in order to restrain the adjacent track erasure or the side erasure.
The magnetic shields as proposed in Document 1 are capable of suppressing the magnetic field from leaking to the adjacent tracks, but may reduce the intensity of the magnetic field that contributes recording on the target track for recording.
Heating the target track for recording as proposed in Document 2 requires laser light to be accurately applied to the target area within the target track for recording. However, it is difficult to align the laser light precisely. Generally, the temperature required to reduce the coercive force of the magnetic layer is 400° C. to 500° C. In practice, it is difficult to instantaneously heat up the hard disk that is rotating at a high velocity so as to reach the above-described temperature. Further, heating may affect other layers in proximity of the recording layer, such as a lubrication layer and a protection layer. More particularly, in the magnetic disk of vertical magnetic recording type, a backing layer of a soft magnetic layer is generally provided to the backside of the recording layer for the purpose of collecting the magnetic fluxes. When the recording layer is heated, the soft magnetic layer is also heated due to thermal conduction, and some problems are concerned. For example, there is a possibility that the capability of collecting the magnetic fluxes of the soft magnetic layer may be lost. When the capability of collecting the magnetic fluxes is lost, information may not be recorded on the recording layer.